The present invention relates to a machine for shrinking heat sensitive film around vacuum packaged food products such as poultry, lunch meats, and the like, wherein said machine delivers and recirculates a hot water medium to effect shrinking of said film in addition to also providing the conveying means whereby said film wrapped products are transported through the machine in order to operationally accomplish a quick and efficient exposure of said heat sensitive film wrapping to the hot water shrinking medium.
In general, shrink wrap packaging of food products within transparent film materials has become a popular and widespread merchandising method in that the same provides a highly protective food product covering, as well as enabling a high degree of consumer visibility of the food product wrapped therein.
In application, the subject food product is either mechanically or manually inserted into or wrapped within an impervious heat sensitive transparent plastic material. By means well known in the art the film wrapper is evacuated and clamped or sealed off, and then, the product thus packaged is introduced to a machine commonly known as a "shrink tunnel", such as those machines respectively shown in U.S. Pat. No. 2,789,407 to Smallegan, dated Apr. 23, 1957, and U.S. Pat. No. 3,678,244 to Worline, dated July 18, 1972, wherein heat, by one means or another, is provided and applied to the packaged product as the same is transported through said machine and the heat sensitive film is thereby shrunk tightly about the product packaged therein. As previously pointed out, the heat may be provided by one means or another, such as by heated water as taught in the patent to Smallegan supra, or, as taught in the patent to Worline supra, a combination of hot air and heated water, or any other suitable means.
It has been determined, however, that in the shrink wrap packaging of food products the heating means employed should be highly efficient so as to permit minimum exposure time of the food product to the heat source while still obtaining acceptable shrinking of the heat sensitive film material about the food product, thereby preventing thermal degradation of the food product by way of a partial cooking, which results in an unattractive discoloration of said food product and thereby defeats the primary purposes of employing a transparent shrink wrap material to provide a highly effective protective food product covering, while at the same time providing high consumer visibility of the food product packaged therein.
Another factor to be considered with regard to thermal degradation of food products during shrink wrap operations is that currently available heat sensitive transparent and translucent film materials, which are generally acceptable in shrink wrap applications for food products, is that said film materials have shrinking temperatures very close to the boiling point of water, which further makes the exposure time during shrinking operations a critical consideration if food product discoloration by way of thermal degradation is to be avoided.
The shrink wrap heating means thus far found to be most generally suitable in terms of efficiency, as well as practical considerations, is heated water and, generally, the heated water is applied to the wrapped food products within the shrink chamber area of the machine by means of a fine spray, or partial immersion, or a combination of both methods.
In the case of fine spray application, the heated water is drawn from a heat exchange reservoir of the machine, pressurized by conventional pumping means, and delivered under pressure to spray nozzles as in the Worline patent, supra. The fine spray method of application gives rise, however, to the following problems. First, since the heated water must be near the boiling point in order to provide effective film shrinking, and while the water is being impelled to a pressure differential through the pumping means, there is frequently steam flashing within the pump casing which either results in a loss of the pumping head, or alternately, a greatly reduced pumping efficiency. Also, the pumping horsepower requirements necessary to operate a pressurized spray application system of the type heretofore described is considerably greater than would otherwise be required if other than conventional high-pressure pumping means were employed. Additionally, the thermal efficiency of the fine spray type application system is relatively low due to the great amount of heat loss by way of the spray cooling effect inherent to the application method. The cone-shaped spray delivered by the spray head of the patent to Smallegan also does not use hot water in a very efficient manner, especially for rapid shrinking.
In the heated water immersion method, although highly effective in causing film shrinking, and highly efficient in heat transfer, there is the problem of obtaining a sufficiently short exposure time so that shrinkage of the film material may be effectively accomplished without also causing thermal degradation and discoloration of the food product wrapped therein.
The shortcomings and limitations set forth in teachings of the previous disclosures are obviated by a substantially improved heat sensitive film shrinking machine which comprises the present invention, the details of which are as follows